The mechanism of venous valve closure. Its relationship to the velocity of reverse flow
P. S. van Bemmelen, K. Beach, G. Bedford and D. E. Strandness Jr
Department of Surgery, University of Washington School of Medicine, Seattle 98195.
Venous valves will close when the reversal of the normal pressure gradient
generates a sufficient reverse flow velocity. By testing 20 healthy
subjects with ultrasonic duplex scanning and controlled limb compression.
It was found that the velocity of reflux is related to the external
compression pressure. Valve closure is an abrupt cessation of reverse flow.
In this study, with subjects in a supine position, valve closure was
achieved only after reverse velocities exceeded 30 cm/s. This velocity was
not generated by manual compression of the limb. With a Valsalva maneuver,
this velocity is achieved only in the common femoral vein in 90% of the
tested individuals. The reflux velocities in response to a Valsalva
maneuver are progressively lower in more distal veins--the profunda
femoris, the superficial femoral vein, and the popliteal vein. With reverse
velocities lower than 30 cm/s, the valves will not close and reflux can
persist. Valsalva's maneuver only allows a diagnosis of valvular competence
at the most proximal level in the venous tree.
